The Mirabilis mosaic virus (MMV) infects Mirabilis plant species (family Nyctaginaceae), a member of the Caulimoviridae family. The virus has a circular double-stranded DNA genome of about 8 Kb with four single-stranded discontinuities in the DNA, one in the alpha strand and three in the complementary strand [1]. The restriction map of the MMV genome is quite different from that of the other members of the genus Caulimovirus [1]. The MMV virus was characterized as a member of the genus Caulimovirus based upon the morphology of its virions and inclusion bodies [2].
Recently, MMV has been fully sequenced, and homology analysis of its genomic DNA has shown that it is a definitive member of the genus Caulimovirus  [Maiti, unpublished]. However, MMV is serologically distinct from the Cauliflower mosaic virus (CaMV), the type species of this genus [2].
Several Caulimoviridae genomes have been fully sequenced and characterized. These include Cauliflower mosaic virus (CaMV) [3], Carnation etched ring virus (CERY) [4], Figwort mosaic virus (FMV) [5], Soybean chlorotic mottle virus (SoCMV) [6], Peanut chlorotic streak virus (PCISV) [7], Casava vein mosaic virus (CVMV) [8], Strawberry vein banding virus (SVBV) [9], Petunia vein clearing virus PVCV) [10], and Mirabilis mosaic virus (MMV) [Maiti, unpublished].
The Caulimovirus genome generally contains two transcriptional promoters, one for the full-length transcript and the other for the subgenomic transcript. These transcripts are equivalent to the CaMV 35S and 19S transcript respectively [6, 11, 12]. A number of strong constitutive promoters have been derived from viruses of the Caulimoviridae family, particularly from the Cauliflower mosaic virus (CaMV): CaMV35S and 19S promoter[13, 14]. Genetic promoters have also been isolated from other members of this family, namely Rice tungro bacilliform virus RTBV) [15], Commelina yellow mottle virus (CYMV) [16], Soybean chlorotic mottle virus (SoCMV) [6], Figwort mosaic virus (FMV, strain DxS) [17, 18]), FMV strain M3 [19], Cassava vein mosaic virus (CVMV) [20], Peanut cholotic streak virus (PClSV) [21] and Mirabilis mosaic virus (MMV) [22, 23] and used for the construction of plant transformation vectors. Transcript promoters from Caulimoviruses, such as CaMV, FMV, PCISV, MMV and FMV are active in all plant organs [13, 18, 21-23], whereas, transcript promoters from Badnaviruses, such as CYMV and RTBV are phloem-specific [15, 16] in expressing genes in transgenic plants.
The CaMV 35S promoter has been well characterized [13, 24-30] and widely used in chimeric gene constructs for heterologous gene expression in transgenic plants [31-33]. The CaMV 35S promoter is also active in bacteria [34], yeast [35], Hela cells [36] and Xenopus oocytes [37].
The expression of useful foreign traits in plants is a major focus in plant biotechnology. There is a need for a variety of different (e.g., constitutive, tissue specific and/or inducible) promoters that meet the different potential applications in this field of plant genetic engineering. Introduction of heterologous genes of interest into plant cells generates the desired qualities in the plants of choice (Maiti and Hunt, 1992; Wagner, 1992). Plant biotechnology is leading a rapid progress in production of economically valuable germplasm with improved characteristics or traits such as insect resistance, virus resistance, fungal resistance, herbicide resistance, bacterial or nematode pathogen resistance, cold or drought tolerance, improved nutritional value, seed oil modification, delayed ripening of fruits, and male sterility, to name a few. These germplasms provide an enhanced development in breeding programs for crop improvement as well as a better understanding of gene regulation and organization in transgenic plants.
Plant metabolic engineering is the application of genetic engineering methods to modify the nature of chemical metabolites in plants. For metabolic engineering where multiple genes need to be inserted into a single cell, the use of different strong constitutive promoters is desirable in order to avoid genetic instability caused by recombination between identical or closely related promoter sequences, for example, those taken from plants themselves. Through use of these promoter sequences the introduced genes can be transcribed to messenger RNA and then translated to resultant proteins to exhibit new traits or characters.
Besides developing useful traits in crops, plant molecular engineering will lead to further understanding of molecular pathways involved in disease development and secondary metabolism in plants. Moreover, by engineering plants with specific foreign genes, the responses of plants to abiotic and biotic stress and stress related metabolism can be analyzed.
Thus, there is a need in the art for plant promoters that can be used to drive the expression of genetically engineered genes in plants.